David Castillo Belio🏹

Humans carry the stomach acid of a vulture, and the scientists who measured it had filed us as omnivores. In 2015 a team from North Carolina State gathered every reliable measurement of stomach acidity they could find, across 68 species of birds and mammals, and lined each one up against what the animal eats. The pattern was clean. Herbivores had the weakest acid. The most specialised plant-eaters went further and grew a separate fermenting chamber, kept alkaline so the microbes breaking down leaves could live in it. Among primates, only one family of leaf-eating monkeys ever built one. Carnivores had stronger acid. Scavengers, the animals eating meat already crawling with bacteria, had the strongest of all. The white-backed vulture sits around pH 1.2. Then humans. Around pH 1.5. Down with the carrion eaters. Other primates sit at 3 or above. Because the scale is logarithmic, that makes the human stomach roughly thirty times more acidic than an ape's. Acid that strong is expensive. The body burns energy making it and burns more protecting its own lining from it. Evolution does not keep paying a bill like that for nothing. The study's verdict was that stomach acid is not there to digest food. It is a filter, a sterilising bath for whatever is coming down. And the strongest filter goes to the animals whose food is most closely related to themselves, because a mammal's bacteria can infect another mammal far more easily than a plant's can. Our acid was built for eating animals, the kind that had been dead a while. Your stomach is set up for a carcass, and the breakfast advice is still porridge.